1. Field of the Invention
The invention relates to a backlight assembly for a hand-held liquid crystal display, and particularly to a backlight assembly that includes a light source mounted onto a flexible printed circuit.
2. Description of the Related Art
With the advancement of Thin Film Transistor Liquid Crystal Display (TFT LCD) technology, TFT LCD has gradually displaced the CRT display and become the mainstream of display technology. TFT LCD has many advantages, such as compact in size and low in power consumption and radiation. It has been widely applied to various types of electronic products, such as PDA, mobile phone, digital video camera, digital camera, notebook computer and television. Since TFT LCD relies on a light source for illumination, a backlight module with sufficient light source is usually provided to meet the requirement.
Refer to FIGS. 1A and 1B for a conventional backlight module for use on a hand-held liquid crystal display (LCD). It includes light guide plate 10, a mold frame 11 and a flexible printed circuit (FPC) 12.
The light guide plate 10 is made from translucent material, such as acrylic. It has a light exit surface 101 on its top side facing a panel (not shown), and a light incident edge 102 on one side adjacent to a light source 14 for guiding the light beam from the light incident edge 102 to the panel via the light exit surface 101. A reflector plate 13 is placed between the bottom surface of the light guide plate 10 and the mold frame 11 for enhancing the brightness by reflecting the reflected or refracted light beams.
The flexible printed circuit 12 has two light emitting diodes (LED) 14 mounted on its top surface serving as the light source. The LED 14 is a luminous semiconductor element made from GaP, GaAs, or the like. When receiving electric current from the flexible printed circuit 12, the LED 14 generates light by transforming the electric energy to optical energy. The number of the LED 14 used depends on actual application. It is not limited to the layout as shown in FIGS. 1A and 1B.
To increase light utilization of the light source, the LED 14 is supposed to attach to the light incident edge 102 of the light guide plate 10. However, in practice a gap may be formed between the light guide plate 10 and the LED 14 due to error tolerance designed for assembly. Consequently, if the gap A is greater than 0.5 mm, loss of the light source could exceed 10% or more. And, a bigger gap A will cause a greater loss of light.
Accordingly, there is a need in the LCD technology to improve the light utilization by eliminating the gap between the light guide plate and the LED.